240 



L. A. ROGERS, W. M. CLARK AND H. A. LUBS 



from bovine feces and from grains. It should not be assumed, 

 however, that the relative numbers of cultures as shown in this 

 chart are indicative of the proportions in which they occur in the 

 intestines. In bovine feces the high ratio or B. aerogenes group 

 occurred so rarely that we obtained only one culture of this type 

 in the 150 isolated. In human feces the proportion of high ratio 

 cultures is usually greater but varies with the individual and 

 perhaps with certain physiological conditions. In only 3 samples 

 were B. aerogenes cultures obtained by direct plating. In one 

 of these, one of seven was B. aerogenes, in another, 3 of 6 and in the 

 third, of 52 colonies subjected to the methyl red test 31 were of the 



/oo% so eo ■^o ^^^ \ 



^o -fo eo so /oo% 



Fig. 3. Physiological Characters of the B. coli Aerogenes Types 



B. aerogenes type. All other high ratio cultures were obtained 

 by special methods. Mr. Ayers called our attention to the fact 

 that when sterile milk was infected with bovine feces and incu- 

 bated at 20° the high ratio type predominated at the time of cur- 

 dling. This holds true also for human feces and the greater part 

 of our high ratio cultures was obtained by plating milk which 

 had been curdled by inoculating with feces and holding at 20° C. 



The predominance of the B. aerogenes type under these condi- 

 tions is probably explained by the observation, made in the course 

 of another investigation, that the B. aerogenes type is less retarded 

 by low temperatures than is the B. coli or low ratio type. 



The fermentation reactions of the two types of cultures are 



